1. Field of the Invention
This invention relates generally to a system and method for determining the position of a rotating wheel using radio frequency identification (RFID) and, more particularly, to a system and method for determining engine crankshaft/camshaft position using RFID tags where the tags are positioned around the perimeter of a crankshaft wheel and/or camshaft wheel.
2. Discussion of the Related Art
As is well understood in the art, an internal combustion engine includes a crankshaft that is rotated by movement of the pistons within the cylinders to provide the driving power. The internal combustion engine also includes one or more intake and exhaust valves per cylinder whose position between open and closed is determined by one or more camshafts. It is necessary that the engine controller know the position of the engine, i.e., the position of the crankshaft and the camshaft, so that it knows when to precisely deliver fuel and spark to each cylinder at the proper time.
Current internal combustion engines typically employ a crankshaft position sensing wheel mounted to a back end of the crankshaft and a camshaft wheel mounted to a front end of the camshaft. The crankshaft wheel and the camshaft wheel include a predetermined number of teeth having a predetermined width with spaces therebetween. A magnetic reluctant sensor or a Hall effect sensor is positioned relative to the wheel that provides an electrical signal on the rising edge and falling edge of each tooth on the wheel. Algorithms are employed that count the pulses from the sensor to provide a precise indication of the position of the engine. The process of determining the position of the crankshaft wheel and the camshaft wheel in this manner is sometimes referred to as pattern recognition. Typically, at least two of the teeth are removed so that the sensor will provide a signal indicating a reference for the start of an engine cycle so that it is properly oriented for each intake, exhaust, and firing of each cylinder.
At vehicle start-up, it is necessary for the engine controller to know the beginning of a cycle before it can initiate the delivery of fuel and spark to the cylinders. Therefore, the crankshaft is rotated by the engine starting system so that when the location of the crankshaft position sensing wheel with the removed teeth is detected by the sensor, the engine controller knows that the cycle can start. However, sometimes this requires a complete revolution of the crankshaft. Further, the sensor may have a fault where it does not immediately pick up the first indication of the reference location of the crankshaft wheel.
Because the position of the engine is determined by pattern recognition in this manner, the start-up of the engine is not immediate upon ignition of the engine because the engine controller must first determine the position of the engine from the removed wheel teeth.